setScorer

Called before successive calls to Collector.collect(int). Implementations
that need the score of the current document (passed-in to
Collector.collect(int)), should save the passed-in Scorer and call
scorer.score() when needed.

acceptsDocsOutOfOrder

Return true if this collector does not
require the matching docIDs to be delivered in int sort
order (smallest to largest) to Collector.collect(int).

Most Lucene Query implementations will visit
matching docIDs in order. However, some queries
(currently limited to certain cases of BooleanQuery) can achieve faster searching if the
Collector allows them to deliver the
docIDs out of order.

Many collectors don't mind getting docIDs out of
order, so it's important to return true
here.